RFID tags are a class of integrated circuits which intercept modulated RF signals from a transmitter (which is normally called a “reader”), demodulate the signal and apply the encoded information to a digital portion of the circuit, and radiate a modulated signal to the reader. The signal typically contains only a small amount of information such as the identification number of the device, although more information may be stored in the tag's memory and may be used either to determine whether the tag responds, or to influence the string of bits which are applied to the modulator. The modulator alters the Q of the antenna and thus its normally re-radiated signal, so no active power is applied to the transmission.
Such tags are intended to be applied to a very large number of objects, for example to shipping boxes or even to the individual items in a store (this application is called “item level tagging”). In order not to unacceptably increase the cost of the objects, the tags have to be very cheap: for item level tagging, for example, the cost to the user is desired to be under 5 ¢.
In order to minimize the total tag cost, each component should be carefully controlled, including the integrated circuit (chip), the antenna, the packaging (substrate and encapsulation), and the process. A typical cost of IC manufacturing for many years has been approximately $4/cm2, or 4 ¢/mm2. Clearly if the IC is 1 mm2 in area, it will not be possible to meet this target. Yet, the RFID chips available, from companies such as Texas Instruments, NXP Semiconductors, Impinj, etc. are typically between about 0.5 and 1 mm2, with most on the high side (or even higher), and actual chip costs (even in high volume) are currently somewhat higher than 4 ¢. Clearly there is a need for smaller, and hence less expensive, chips.